In recent years, as an illumination-purpose light source, attention is paid to a surface light-emitting source using an organic EL (electroluminescence) element. For example, Japanese Patent Application Publication No. 2011-243461 discloses a lighting device using an organic EL panel as a surface light-emitting source.
In the conventional example of Japanese Patent Application Publication No. 2011-243461, a surface light-emitting module having an organic EL panel and an accommodation portion for accommodating the surface light-emitting module with little clearance are arranged in a device body. A positive power-feeding terminal and a negative power-feeding terminal connected to an external power supply through an electric circuit are provided in two opposing sides of a bottom surface of the accommodation portion. Protrusions engageable with locking holes formed at the opposite ends of lateral surfaces of the surface light-emitting module are formed on two opposing inner surfaces of the accommodation portion. A hook-shaped locking piece capable of moving into and out of the accommodation portion is provided on one of the two opposing inner surfaces of the accommodation portion. The locking piece is normally biased by a spring in such a direction as to protrude from one inner surface of the accommodation portion. An operation piece for displacing the locking piece against the biasing force of the spring and retracting the locking piece inward of the inner surface of the accommodation portion is arranged around the accommodation portion.
Accordingly, if the protrusions arranged inside the accommodation portion come into engagement with the locking holes formed in the arbitrary corners of the surface light-emitting module, the surface light-emitting module is connected to the device body through the protrusions and can rotate about the protrusions as a rotation axis. Thereafter, if the surface light-emitting module is rotated toward the accommodation portion, the other surface of the surface light-emitting module makes contact with the locking piece. If the surface light-emitting module is further rotated toward the accommodation portion, the locking piece is pushed inward of the inner surface of the accommodation portion against the biasing force of the spring, whereby the surface light-emitting module is accommodated within the accommodation portion. A locking groove for receiving the locking piece is formed on each of the lateral surfaces of the surface light-emitting module. If the surface light-emitting module is accommodated within the accommodation portion in this manner, the locking piece normally biased by the spring protrudes again into the accommodation portion and comes into the locking groove. As a consequence, the surface light-emitting module is held by the protrusions at one side and by the locking piece at the other side, whereby the surface light-emitting module is fixed inside the accommodation portion.
When removing the surface light-emitting module from the device body, the operation piece is slid and the locking piece is retracted against the biasing force of the spring. Thus the surface light-emitting module is detached from the locking groove. In case where the device body is attached to a ceiling, the surface light-emitting module is rotated downward by the weight thereof. As a result, a gap is generated between the surface light-emitting module and the accommodation portion, whereby the surface light-emitting module can be removed from the device body.
In the conventional example of Japanese Patent Application Publication No. 2011-243461, if a strong vibration is applied to the device body due to an earthquake or other causes, there is a possibility that the surface light-emitting module is moved against the biasing force of the spring and the locking piece is disengaged from the locking groove. In the event that the locking piece is disengaged from the locking groove, the surface light-emitting module may possibly be dropped from the accommodation portion of the device body.